Hair transplantation procedures are well-known, and typically involve harvesting donor hair grafts, for example, from the side and back fringe areas of the patient's scalp (“donor areas”), and implanting the harvested grafts in a bald area (“recipient area”). Historically, the harvested hair grafts were relatively large (3-5 mm), although more recently the donor grafts may be single “follicular units,” which are naturally occurring aggregates of 1-3 (and much less commonly, 4-5) closely spaced hair follicles that are distributed randomly over the surface of the scalp. In one well-known process, a linear portion of the scalp is removed from a donor area by dissection, using a scalpel to cut down into the fatty subcutaneous tissue. The strip is dissected (under a microscope) into the component follicular units, which are then implanted into a recipient area in respective puncture holes made by a needle. Forceps are typically used to grasp and place the follicular unit grafts into the needle puncture locations, although other instruments and methods may also be used.
In “Androgenetic Alopecia” (Springer 1996), M. Inaba & Y. Inaba disclose and describe a method for harvesting singular follicular units by positioning a hollow punch needle having a cutting edge and interior lumen with a diameter of 1 mm, which is about equal to the diameter of critical anatomical parts of a typical follicular unit. The needle punch is axially aligned with an axis of a follicular unit to be extracted and then advanced into the scalp to cut the scalp about the circumference of the selected follicular unit. Thereafter, the follicular units are easily removed, e.g., using forceps, for subsequent implantation into a recipient site with a specially devised insertion needle.
U.S. Pat. No. 6,585,746 (Gildenberg) discloses using a robotic system for hair transplantation, the system including a robotic arm and a hair follicle introducer associated with the robotic arm. U.S. Patent Publications 2007/0078466 and 2007/0078475, which are each assigned to Restoration Robotics, Inc., of Mountain View, Calif. (assignee of the present application), also disclose automated (e.g., robotic) systems used for transplanting hair follicular units, including a multi-part tool assembly carried on a robotic arm. The tool assembly is independently controllable relative to the robotic arm, and includes an inner, “harvesting” cannula with a longitudinal axis that is automatically aligned (under image-guidance) with a selected follicular unit to be harvested from a donor area of a body surface, and then advanced relative to the body surface so that an open, tissue coring distal end of the harvesting cannula penetrates the body surface surrounding the selected follicular unit to a depth sufficient to substantially encapsulate the follicular unit. The harvesting cannula is then withdrawn from the body surface with the follicular unit engaged by and retained in an interior lumen thereof. An outer, “implanting” cannula is disposed coaxially over (and moveable relative to) the harvesting cannula, wherein a tissue piercing distal end of the implanting cannula is used to puncture a recipient area of the body surface and form an implantation cavity, with the follicular unit displaced from the harvesting cannula lumen into the implantation cavity.
Some manual and partially automated devices for hair harvesting and transplantation that are known in the art include, for example, the use of a vacuum source to assist in extracting hair follicles from a body surface. However, it has been determined that during the harvesting procedure, the vacuum source may not always provide enough “grasping” force to fully extract the follicular unit from the body surface. For example, tissue strands may sometimes tether the follicular unit to the scalp as the follicular unit is being retracted from the scalp, and can end up pulling the follicular unit out of the harvesting cannula, even against the force of the vacuum source. In addition, the pulling force of the tissue strands may damage the follicular unit, even if it breaks free from the scalp.